P.O. Box Ratio Constantan Coil Manufacturer,Supplier and Exporter in India
Product Code : EL-SI-8134
Jlab Export is a leading P.O. Box Ratio Constantan Coil Manufacturer,and suppliers in India
P.O. Box Ratio Constantan Coil (code EL-SI-8134) is a Post Office box–type resistance box for Wheatstone bridge experiments in school and college physics labs. Its coils are wound with constantan to an accuracy within ±0.1% and are fixed to 14 mm thick rectangular brass blocks; it is listed as P.O. Box Ratio 3 and P.O. Box Ratio 4. It is made by Jain Laboratory Instruments Pvt Ltd (JLab) at its works in Ambala, India.
Specifications
| Parameter | Detail |
|---|---|
| Coil wire | Constantan |
| Coil accuracy | Within ±0.1% |
| Blocks | Rectangular brass blocks, 14 mm thick |
| Versions listed | P.O. Box Ratio 3 (14 mm) and P.O. Box Ratio 4 (14 mm) |
| Quality check | Each box is visually inspected before dispatch |
| Pack quantity | Each (sold individually) |
| Minimum order quantity | 10 units |
| Dispatch time | Usually 7–10 working days |
| Product code | EL-SI-8134 |
| Manufacturer | Jain Laboratory Instruments Pvt Ltd (JLab) — OEM |
| Country of origin | India (made in Ambala, Haryana) |
How Does It Compare with Other JLab P.O. Boxes?
| Model | Coil wire | Listed accuracy | Brass blocks |
|---|---|---|---|
| This box (EL-SI-8134) | Constantan | Within ±0.1% | 14 mm thick, rectangular |
| P.O. Box Ratio Manganin Coil | Manganin | ±0.02% to 0.005% | 14 mm thick, rectangular |
| Resistance P.O. Box | Constantan | +0.1% (as listed) | 12 mm thick, rectangular |
The constantan box suits routine teaching practicals; choose the manganin version where a closer coil tolerance is required.
What Is the P.O. Box Used For?
A Post Office box is a Wheatstone bridge built into one box of plug-in resistance coils. With a cell, a galvanometer and two tapping keys connected, students set the ratio arms, adjust the third arm until the galvanometer shows no deflection, and calculate an unknown resistance, then go on to the resistivity of a wire. Constantan is used for the coils because its resistance changes very little as it warms. Keep the plugs clean and seat them firmly with a slight twist, as a loose plug adds contact resistance, and press the battery key before the galvanometer key.
Frequently Asked Questions
What are the coils made of, and how accurate are they?
They are wound with constantan and are listed as accurate within ±0.1%.
Which versions are available?
P.O. Box Ratio 3 and P.O. Box Ratio 4, both with 14 mm brass blocks. The listing does not give the coil values of each, so ask JLab to confirm them before ordering.
How is it different from the manganin coil P.O. box?
The manganin version shares the 14 mm rectangular brass blocks but is listed with a closer accuracy of ±0.02% to 0.005%.
Who manufactures it?
JLab (Jain Laboratory Instruments Pvt Ltd) makes the box at its works in Ambala, Haryana, India.
OEM Manufacturer
JLab is the trading name of Jain Laboratory Instruments Pvt Ltd, a physics lab instruments manufacturer in India, incorporated in 2017 and based on Hargolal Road, Ambala, Haryana. The P.O. box is wound and assembled in JLab’s own works, so schools, colleges, dealers and importers buy it direct from the maker, and every box is visually inspected before dispatch. JLab exports worldwide and ships to buyers in every region — Italy in Southern Europe, Honduras in Central America and the Caribbean, Namibia in Southern Africa, Estonia in Northern Europe and Tunisia in North Africa, for example. Tender details are on the JLab lab tenders page.
For Wheatstone Bridge Practicals
- P.O. Box Ratio Manganin Coil — the closer-tolerance manganin version.
- Resistance P.O. Box — constantan-coil P.O. box with 12 mm brass blocks.
- Galvanometer — the null detector for bridge practicals.
- Tapping Key — momentary-contact keys for the battery and galvanometer circuits.
- Portable Wheatstone Bridge — a self-contained bridge with decade dials and a built-in galvanometer.
See the Scientific Instrument range and the Indian Instruments section.
Request a Quote
Quotes come direct from the manufacturer. Use the Add To Cart enquiry button, or send the version (Ratio 3 or Ratio 4), the quantity (minimum 10 units) and the delivery location through the contact page.
Last updated: 8 October 2026
